While operating a punch press it is necessary to transfer blank sheets of material into and out of the punch press. Such operations are often done in high speed production facilities. In order to maximize production capabilities of a particular assembly line, loading and unloading the punch press has been automated by using computer controlled robots that are capable of handling stock material. Other systems for feeding a press include a holding bin feed system which has an automatic sheet feeding mechanism that incorporates a device for picking up the top sheet of blank material and advancing the blank sheet to a feed or work table. The feed mechanism then advances the blank sheet to a set of punch press grippers and against the alignment pins within the press. Once the blank sheet is properly located within the press, the press performs its operation and the stamped sheet is removed and the cycle repeats.
One of the problems with the aforementioned conventional automatic sheet feed type mechanisms is that if more than one blank is fed into the press, the press can be damaged, thus resulting in significant down time and repair costs. Further, if the holding bin containing the stock of blank sheets is empty and no blanks are fed into the punch press, then the press would cycle but not produce any finished product because no blank sheet was fed into the press. This results in a waste of time and can contribute to other problems on the assembly line.
Accordingly, it is desirable to provide a method and apparatus for detecting the presence of more than one blank that is to be introduced into a press prior to the press cycling. In such a double blank situation it would be desirable to stop the press from cycling and to notify the press operator of this undesirable condition.
It would also be desirable to provide a method and apparatus for determining whether no blank sheet of material is being advanced to the punch press. Such condition could occur when the supply stack of blanks from the holding bin has been depleted. In such a condition it would be desirable to stop the press from cycling and notify the press operator of this undesirable condition.
According to one aspect of the present invention, a system for detecting blanks that are being fed to a machine is comprised of a first cylinder connected to a frame member and operable to be situated to a first position and to a second position. A second cylinder is connected to a frame member and is operable to be situated to yet another first position and to a second position. A pivoting jaw member is connected to the frame member and to the second cylinder. A fixed jaw is further connected to the frame member and is spaced apart from the pivoting jaw member to create a receiving area for receiving a steel blank. An indicator bar pivots relative to the pivoting jaw member which in turn advances to a position in accordance to the number of blanks positioned between the fixed pivoting jaw. The indicator bar interrupts a light beam generated by an infra-red light system when one blank is detected.
According to another aspect of the present invention, a process of detecting a condition when other than one blank is being fed into a press is comprised of the steps of positioning a first cylinder to a retracted position and a second cylinder to an extended position. A steel blank is advanced to a check position located between a pivoting and fixed jaw. The first cylinder then extends while the second cylinder is retracted. An indicator bar that is pivotally connected to the pivoting jaw is then advanced to a position where it either interrupts a light beam or does not interrupt the light beam. The resulting condition is sensed by a receiver and a signal is transmitted to a control box where the signal is processed. If the light beam signal is interrupted by the indicator bar, a signal is produced allowing the press to continue operating. Alternatively, if the light beam is not interrupted, then a corresponding signal is produced thus stopping the press from cycling and notifying the operator of this condition.
These and other various advantages and aspects of the present invention will become apparent from the following description and claims, in conjunction with the patent drawings.